Directions : In the following question more than one of the answers given may be correct. Select the correct answer and mark it according to the code:
Clay and organic matter of the soil have negative charges. They attract positively charged ions like: (1)\[C{{a}^{2+}}\] (2) \[M{{g}^{2+}}\] (3)\[{{K}^{+}}\] (4) \[A{{l}^{3}}\]A) 1,2 and 3 are correct
B) 1 and 2 are correct
C) 2 and 4 are correct
D) 1 and 3 are correct
Correct Answer: A
Solution :
Ionic exchange is the exchange of ions between a cell or root and the external medium. Positively charged ions or cations (\[e,g.,\,{{K}^{+}},C{{a}^{++}},M{{g}^{++}}\]) are exchanged with PT ions while negatively charged ions or anions (\[e,g.,C{{1}^{-}},NO\,_{3}^{-},\,SO\,_{4}^{--}\] are exchanged with \[NO_{{}}^{-}\] or \[HCO\,_{3}^{-}\] ions. Ionic exchange between root and soil can occur by two methods: Carbonic add exchange: \[C{{O}_{2}}\]produced in respiration dissolves in water to form carbonic add. Carbonic add dissociates into hydrogen (H+) and bicarbonate (\[HCO\,_{3}^{-}\]) ions. \[{{H}_{2}}O+C{{O}_{2}}{{H}_{2}}C{{O}_{3}}{{H}^{+}}+HCO\,_{3}^{-}\] \[{{\mathbf{H}}^{\mathbf{+}}}\mathbf{,OH}{{\,}^{\mathbf{-}}}\,\mathbf{or}\,\mathbf{HCO}\,_{\mathbf{3}}^{\mathbf{-}}\] ions absorbed over the surface of root can directly get exchanged with similarly charged ions present over the surface of soil particles if their oscillation volumes overlap.
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